Murder or suicide? The death of the preacher's wife

[This story previously aired on July 30, 2011. It was updated on May 25, 2013.]

Ever since Matt Baker's wife, Kari, died suddenly at the age of 31, the Baptist preacher has lived under a cloud of suspicion. Is he an innocent man unfairly accused as his followers and friends believe? Or is he hiding a terrible, dark secret?

"I know if she were sitting here she would look at you and say 'He didn't do anything. Leave him alone.' But she can't," Matt told Baker "48 Hours" correspondent Erin Moriarty. "It's so improbable. It's not who I am. I loved my wife. I never hurt her a day in my life."

Kari was a popular third-grade teacher. She and Matt had been together since meeting as counselors at a Baptist day camp in Waco, Texas, in 1994.

"I would have been 23 and she was 20," Baker recalled. "I met her and I thought, 'This is the person for me.'"

Linda and Jim Dulin remember their daughter was instantly smitten with the Baylor University senior. "The thing she kept talking about was, 'Mom, this guy's a really good Christian,'" said Linda Dulin.

And just three months after meeting, Matt and Kari suddenly announced they were getting married. By their first anniversary, Kari was pregnant with daughter Kensi; a second daughter, Kassidy, followed a year-and-a-half later.

"She loved her girls," Linda said. "You know, you know how you feel. There are no words."

But right after Kassidy's first birthday, doctors discovered a brain tumor and she was hospitalized. "There'd be days that it looked really good. Prognosis was good. And then turned around and went right back down hill," Baker explained.

In late February 1999, after a 90-day bedside vigil, Kassidy was well enough to go home. But just after midnight on March 22, Kassidy was rushed to the emergency room. This time doctors couldn't save her.

"To sit there and struggle that far. To come what I thought was so far to watch her die... that was devastating. It really was a very hard, hard thing to cope with," Baker told Moriarty.

It was especially hard for Kari. "She lost her child and she grieved hard," said Linda.

A grief counselor helped Kari get through the first year. In 2000, a third daughter, Grace, was born. But according to Matt Baker, his wife was never the same.

"I don't think it was a split second, all of a sudden she was completely different. It was a gradual changing of the person," he explained. "She had - almost two personalities in a way. Not negative. But when she went to work she had the ability to put issues behind her and focus on work."

"The other personality was a little bit more withdrawn at home," Baker added.

The way Matt Baker tells it, he became "Mr. Mom" to Kensi and Grace. And from the time Kassidy died, Baker said his wife relied on pills to sleep.

According to Baker, Kari used Unisom, an over-the-counter sleep medication. But he said she sometimes borrowed something stronger from family and friends.

And the toughest time for Kari was always the March anniversary of Kassidy's death.

"It was always two or three weeks leading up to it. 'It's coming, it's coming. I can't do this. I can't make it another year. I can't do this again,'" said Baker.

In April 2006, seven years after Kassidy died, Matt said Kari was still struggling with the loss. So he took her to the doctor, who diagnosed her as depressed and prescribed an antidepressant.

"And about that time my wife started almost hyperventilating again in the office. Didn't like him saying anything about depression," Baker explained. "She would never agree that that could be a problem."

As they left the clinic and headed onto the highway, Baker said Kari had a meltdown.

"And I'm at about 45, 50 mph and she is hyperventilating. And she attempts to open the car door as we are driving down the road," he said. "She said she needed to get out, get some air."

According to Baker, he grabbed hold of Kari's waistband until he could pull off the highway. He didn't think it was a suicide attempt. "I thought she just wanted fresh air and wasn't thinking. She lost it for a second," he said.

Later that week, on Friday, April 7, Kari had a crucial interview for a new job at a junior high school; Baker described Kari's mood as "nervous."

And after the interview, Baker said Kari didn't feel well. That evening, despite a queasy stomach, he said Kari drank a wine cooler.

At 10:30 p.m., with the kids in bed, Baker said Kari asked him to gas up the car and rent a movie.

"And I thought, 'It's late. All right, but I'll do it. If your wife asks you, do what your wife asks.' And so I got dressed and left the house a little after 11:00," he recalled.

"It's probably about two miles to the first gas station that I could fill up at. And got out. Pumped the gas ... Went up to the movie place. Rented a movie ... and drove back home."

When he returned around midnight, Baker said he found the bedroom door was locked.

"And so I go and I get the little screwdriver that can fit in there and I popped the button. Open the door... And she's naked on the bed," Baker explained. "And I call her name and she doesn't respond."

At 12:01 a.m. he called for help. "And as I'm calling 911 I'm deciding I don't want them to see her naked. So I put her clothes on her," he told Moriarty.

Matt Baker said at the same time he was on the phone, he was also moving Kari to the floor where he began CPR. Paramedics arrived within minutes, but it was too late. Kari was dead.

Police found an empty bottle of Unisom next to a note. "I am so sorry," it read, "I love you Matt ... I want to give Kassidy a hug. I need to feel her again."

It was all the evidence the small town police needed.

"The detective that night -- pulled me into the kitchen. He goes, 'Well, she took her own life. There's a note. There's pills... There's no signs of struggle. It's pretty obvious what happened.' And that point my heart sunk. I couldn't believe it. That was the first time for sure that's what they claimed it to be," said Baker.

"We were truly in shock," Linda Dulin said of her daughter's death. "It was almost like we were in a trance. And all I kept thinking about - all Jim kept thinking about was that we didn't have a daughter. Our daughter was gone."

The county doesn't have a medical examiner, so police described the scene over the phone to a justice of the peace, who determined that Kari died from an "overdose of Unisom." No autopsy needed. Two days later, she was buried.

And that might have been the end of the story if not for a group of tenacious women.

"We wanted to clear Kari's name," Kari's aunt, Nancy, told Moriarty. "Matt was going around talking about what a depressed, suicidal person she was. We knew she wasn't."